Magnetic domain propagation arrangement



C. 13, 1970 A, H, BQBECK 3,534,346

MAGNETIC DOMAIN PROPAGATION ARRANGEMENT Filed May 28, 1968 2Sheets-Sheet 2 United States Patent O" 3,534,346 MAGNETIC DOMAINPROPAGATION ARRANGEMENT Andrew H. Bobeck, Chatham, NJ., assignor to BellTelephone Laboratories, Incorporated, Murray Hill, NJ.,

a corporation of New York Filed May 28, 1968, Ser. No. 732,704 Int. Cl.G11c 13/00, 19/00 U.S. Cl. 340-174 9 Claims ABSTRACT F THE DISCLOSURE Asingle wall domain is propagated, in a sheet of magnetic material, alongan axis aligned with a single conductor in which a current signal ows. Achannel of propagation for the domain is defined by a soft magneticoverlay which has a zig-zag configuration defining stable positions fordomains alternative ones of which are on opposite sides of theconductor. The positions to one side of the conductor are stable domainpositions for one polarity of current; the positions to the other sideare stable domain positions for the opposite polarity of current.Directionality of domain movement is provided by asymmetry in theoverlay pattern or by a directional field in the plane of the sheet. Auniform bias field maintains the domains at a prescribed diameter. Shiftregister operation is achieved in the absence of discrete propagationconductors.

FIELD OF THE INVENTION This invention relates to domain propagationarrangements and, more particularly, to arrangements in which singlewall domains are propagated in a sheet of magnetic material.

BACKGROUND OF THE INVENTION Single wall domains are reverse-magnetizedregions encompassed `by a domain wall which closes on itself to form,illustratively, a cylindrical geometry the diameter of which is afunction of the material parameters. Inasmuch as the boundary of thedomain is independent of the boundary of the sheet, multidimensionalmovement of the domains can be realized.

A simple convention permits the visualization of single wall domains.Most sheets of material in which single wall domains can be moved arecharacterized by a preferred direction of magnetization substantiallynormal to the plane of the sheet. We may adopt the convention thatpositive and negative directions for the magnetization are up out of anddown into the plane of the sheet respectively. A single wall domain inthis context may be visualized as an encircled plus sign and themagnetization in the remainder of the sheet may be represented by minussigns. The Bell System Technical Journal (BSTJ), volume 46, No. 8,October 1967, pages 1901 et seq., describes single wall domains, variousoperations employing the movement of single wall domains, and suitablematerials in which those domains can be moved.

Selective movement of a single wall domain is realized normally by thegeneration of a localized attracting field (viz., field gradient) at aposition offset from the position occupied by a domain. In accordancewith the assumed convention, a discrete conductor in the form of a loopcoupled to a position offset from that occupied by a domain generates anappropriately placed localized positive field (up out of the plane) whenpulsed. The domain moves to the position of the loop in response.

When an attempt is made to miniaturize single wall domain devices, it isrealized that single wall domains can be obtained with geometries farsmaller than the smallest dimensions realizable for the circuitryrequired to move "Ice them. There are a variety of reasons for this. Theloop shape geometry of a discrete propagation conductor, for example,occupies more space than say a single conductor. Moreover, drive wiringeconomy and the need to provide directionality in the propagationchannels dictate three-phase propagation operation pulsing as is Wellunderstood. Consequently, only one position in three may be occupied bya domain in practice although the positions may overlap one another.Further, drive current requirements dictate minimum cross sectionalareas for conductors. But photo deposition techniques do not permitclosely spaced conductors to have disproportionate widths andthicknesses Without risking short circuits between adjacent conductors.As a result, as much as ten mils is allocated per bit location, yetdomains of the order of microns can be realized. Discrete propagationconductors cannot be eliminated entirely either without reducing thecapability of moving domains selectively.

An object of this invention is to provide a domain propagationarrangement in which single wall domains can be propagated in theabsence of discrete propagation conductors and in which domain movementalong selected channels can be realized.

BRIEF DESCRIPTION OF THE INVENTION The invention is based on thediscovery that a variety of overlay patterns, of a soft magneticmaterial such as permalloy, on the surfaces sheets of magnetic materialin which single wall domains can be moved, exhibit changing magneticpole patterns in response to changing magnetic fields. It has been foundfurther that these overlay patterns can be chosen so that single walldomains can tbe made to follow the changing pole patterns from input tooutput positions in the absence of discrete propagation conductors.Moreover, the pole-changing fields can be provided in a manner to permitchannel selection for domain movement.

In one embodiment, zig-zag shaped permalloy overlays are deposited on asheet of thulium orthoferrite between input and output positions forsingle wall domains. A conductor is aligned with the axis of eachzig-zag overlay. Bipolar pulses applied to a selected conductorygenerate in the associated overlay a changing pole pattern which isfollowed by domains only in the selected channel. Directionality indomain movement is determined by asymmetry in the shape of the overlayor by a direction determining field in the plane of the sheet.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a schematic representation ofa domain propagation arrangement in accordance with this invention;

FIGS. 2A, 2B, 2C, and 2D are schematic illustrations of a portion of thearrangement of FIG. 1 showing consecutive domain positions duringoperation;

FIG. 3 is a pulse diagram of the operation of the arrangement of FIG. l;and

FIG. 4 is a schematic representation of an alternative domainpropagation arrangement in accordance with this invention.,

DETAILED DESCRIPTION FIG. 1 shows a domain propagation arrangement 10 inaccordance with this invention. The arrangement cornprises a sheet 11 ofa material in which single wall domains can be moved along propagationchannels between input and associated output positions.

Overlays 12 define propagation channels for domains in sheet 11. Eachoverlay pattern has a generally zig-zag geometry shown schematically inFIG. 1 and in more specific detail in FIG. 2A. Each zig-zag geometry isaccompanied by a conductor 13 which is aligned with the axis of theassociated zig-zag pattern and positioned illustratively between overlay12 and sheet 11. The conductors 13 are connected between a channelselect circuit 14 and ground. The channels are designated C1, C2, C3,and CN as shown in FIG. 1.

The input positions to the various channels are shown to the left of thezig-zag patterns in FIG. l. The positions are dened by the extended tipsof a large domain 15 of positive magnetization in accordance with theassumed convention. fI-Iairpin conductors 16C1, 16C2, 16C3, and 16CNintersect the extended tips and serve to sever those tips, when pulsed,to provide domains for propagation in the associated channels.Conductors 16 are connected between an input pulse source 17 and groundfor selective operation thereof.

The geometry of large domain 15 is maintained by a conductor 15Aconnected between a D C. source S and ground. The conductor 15A outlinesdomain 15 and generates a positive field in the region of that domain.This operation is disclosed in copending application Ser. No. 579,931led Sept. 16, 1966, now Pat. No. 3,460,1116, for A. H. Bobeck, U. F.Gianola, R. C. Sherwood and W. Shockley.

The output positions are to the right of the zig-zag overlays as viewedin FIG. l. The output positions are defined by a conductor 18 whichcouples serially the terminal positions to the extreme right of theoverlays. Conductor 18 serves to collapse domains occupying any of theso-coupled positions when the conductor is pulsed. Conductor isconnected between an interrogate pulse source 19 and ground.

A plurality of output conductors couple the output positions also. Theoutput conductors are designated OCCl, OCCZ, OCC3, and OCCN tocorrespond to the associated channel designations. Each of the outputconductors is connected between a utilization circuit 20 and ground.

For domain movement in accordance with this invention, a specifieddiameter for each single wall domain is maintained. A bias field isprovided for this purpose. This bias field is normal to the plane ofsheet 11 in a direction to contract domains. In keeping with the adoptedconvention, the bias field is negative, that is to say, directeddownward into sheet 11. The bias field is generated conveniently by acoil (not shown) encircling sheet 11 and lying in the plane of thesheet. Alternatively, a permanent magnet may be used for this purpose.Block 21, designated bias source represents the source of such a field.

The various sources and circuits are connected to a control circuit 22for synchronization and energization. Such sources and circuits may beany such elements capable of operating in accordance with thisinvention.

IFIGS. 2A, 2B, 2C, and 2D show the consecutive positions to which adomain D is propagated in accordance with this invention. We will assumean arbitrary starting position for the domain in FIG. 2A in anillustrative propagation channel C1. To avoid confusion, a domain isrepresented as a circle without a plus sign. The plus and minus signsshown in FIGS. 2A-2D indicate pole concentrations only.,

Although generally of a zig-zag geometry, the magnetic overlay patternis shown in FIG. 2A, illustratively, as having an additional curved areaat each position therealong where its slope changes direction. Thedomain D in FIG. 2A is shown mating with one such curved area. Thecurved areas serve as stable positions for domains. The geometry of theoverlay 12, specifically, permits domain movement only in the prescribeddirection from stable position to stable position illustratively becauseof its asymmetrical shape. For the geometry shown, movement is to theright as viewed in FIG. 2A.

The contribution of the asymmetry of the overlay may be understood asfollows. When a current ows in a conductor 13, negative and positivepoles are generated in the associated overlay as is clear from thefamiliar right-hand rule. These poles are indicated fully to the rightin FIG. 2A. For the convention adopted and for the assumed relativepositions of overlay 12, conductor 13, and sheet 11, negative polesattract a domain and positive poles repel a domain. A domain introducedat the left in FIG. 2A tends to move upward toward the negative chargesand away from the positive charges always remaining essentiallyunderneath the overlay. But the diameter of the domain is chosen to beabout the same size as the width of the overlay. Therefore, the domaindoes not move fully away from the positive charges because of thegeometry of the overlay but, rather, moves to the right, as viewed, toincreasingly negative positions.

The curved area in which domain D is shown in FIG. ZA is the mostnegative available position for a domain introduced from the left asshown in the figures. The domain can move no further to the rightwithout moving to a relatively positive position.

On the other hand, when the current in conductor 13 reverses, asindicated by the arrow z' in FIG. 2B, the pole distribution changes.Domain D again moves to increasingly negative positions. But thenegative positions are now below wire 13 as viewed in FIG. 2B. Movementis again to the right because the asymmetrical geometry of the overlayprovides the nearest increasingly negative path in that direction. Thedomain moves until it occupies the next stable position as shown in FIG.2B.

lFurther alternations of the current applied to conductor 213 produceschanging -pole patterns which attract a domain to correspondingpositions as shown in FIGS. 2C and 2D and eventually attract the domainto an output position for detection.

:Of course, more than one domain can be moved along a propagationchannel. All such domains move synchronously in response to thealternations in current in conductor 13. The domains may occupy, forexample, the positions of next adjacent (negative) curved areas in FIG.2A. Information is represented by the presence (binary one) and absence(binary zero) of domains. A domain pattern so representing informationalso moves synchronously in a propagation channel.

The input implementation is synchronized with the propagation currentalternations in conductor 13. Thus, a pulse appears on a selected inputconductor, say 16C1 of FIG. 1, severing a domain from a large domain 15when the closest stable position (curved area) of the overlay 12 ofchannel C1 is, say, negative as shown in FIG. 2A. If a pulse is absentat that time on conductor 16C1, the absence of a domain is provided forpropagation. The absence of a domain is represented as a broken circlein FIG. 2A.

The output is synchronized with the propagation current alternations inconductor 13 also. For example, control circuit 22 activates pulsesource 19 for pulsing interrogate conductor 18 to collapse any domainsin output positions. Circuit 22 enables utilization circuit 20synchronously. If a domain is present in an output position, a pulse isapplied to circuit 20 by means of the corresponding output conductorOCCl.

FIG. 2A shows the domain pattern for the information 1 0 1. Theinformation is introduced by pulses P16C1 applied selectively toconductor 16C1 at times t0 and t2 in the pulse diagram of FIG. 3. Attime t1 in that figure, a pulse P16C1 is absent as shown by the brokenpulse form there. The pulses can be seen to be synchronized with thepositive alternations of the pulses -l-P13 in conductor 13. Theconductor 13 for channel C1 may be pulsed selectively by input source 17under the control of control circuit 22 for achieving selective movementof information in channel C1.

Asymmetry in the overlay pattern is not the only implementation forachieving directionality in domain movement. A directional field Hd maybe provided in the plane of sheet 11 instead. The directional eld isaligned with the conductors 13. The direction of that field isdeterminative of a net displacement of domains in the absence ofasymmetry in the overlay pattern as alternatively poled pulses areapplied to a conductor 113. The directional field is represented by thedouble-headed arrow, also designated Hd, aligned with conductors 13 inFIG. 1. The field is generated by a magnet or a coil oriented normal tosheet 11 as is well understood in the art. Block 25 in FIG. 1 designateddirectional field source represents an appropriate implementation.Copending application Ser. No. 726,454, filed May 3, 1968, now PatentNo. 3,518,643 for A. J. Perneski discusses one suitable implementationin greater detail.

The conductors 13 of FIG. l, of course, can be oriented in a directionperpendicular to the orientation shown for them in FIG. 1. Moreover, theconductors and the associated overlays can be oriented in eitherdirection in one implementation to permit domain propagation selectivelyin either of two perpendicular directions. This latter implementationrequires both X and Y channel select switches designated 14X and 14Y inFIG. 4. A domain D in FIG. 4 accordingly finds itself in each of an Xand a Y channel in each instance. Propagation of a domain in eitherchannel proceeds as described above.

The conductor and overlay patterns intersect as shown in FIG. 4, thoseelements oriented in one direction conveniently being disposed on asurface of sheet 11 opposite to that on which the elements in the otherorientation are disposed. Only negligible interactions are present dueto the overlays in one orientation on domains being propagated in theother. Alternatively, the X and Y oriented overlays can be disposed on asingle surface of sheet 11. In this arrangement, like oriented portions(30, FIG. 4) of the two overlays may be formed as a single commonportion.

If a directional field is employed rather than asymmetry in the magneticoverlays for achieving domain directionality, a means, similar to thatrepresented by block 25 of FIG. 1, is provided for generating fieldsiHdX and iHdY as shown in FIG. 4. Such a means may comprise mutuallyorthogonal Helmholtz coil pairs disposed normal to the plane of sheet 11in FIG. 1 with appropriate switching means. Such an implementation iswell understood iu the art and is not shown or discussed further herein.The above-mentioned copending application of A. I. Perneski discusses asuitable implementation in greater detail.

It has been found that domains may occupy stable positions spaced apartabout three domain diameters. Since domains on the order of a micronhave been observed, packing densities of more than a million bits persquare inch are realizable in the absence of discrete propagationconductors. Photoresist techniques are sufficiently controlled to permitthe realization of such packing densities with overlays and conductorshaving geometries of the type disclosed.

The relationship of about three to one between the repeat of the overlaypattern of FIG. 1 and a domain diameter is supported by the followingexample: Three mil diameter domains are moved in a sheet of thuliumorthoferrite in the manner described in connection with FIG. 1.Magnetically soft permalloy overlays 2,500 angstrom units thick definepropagation channels for the domains. The repeat for the overlay isabout mils. Conductor 13 has a diameter of about one mil and currents ofabout 100 milliamperes are applied to generate suitable pole patternsfor effecting domain movement.

The overlay 12 may comprise any material which supports suitable polepatterns. Any high permeability thin magnetic lm or a film havingrelatively low coercivity and anisotropy to permit switching of uxtherein by the external fields characteristic of magnetic domains issuitable. A typical material is a magnetically soft Permalloy.

What has been described is considered only illustrative of theprinciples of this invention. Numerous other arrangements in accordancewith the principles of this invention may be devised by one skilled inthe art without departing from the spirit and scope thereof.

What is claimed is:

1. A domain propagation arrangement comprising a sheet of material inwhich single wall domains can be propagated, bias -means for providingin said sheet a bias field of a polarity to contract domains to aspecified geometry, a first electrical conductor contiguous sai-d sheet,means for applying positive and negative currents to said firstconductor, and a first magnetic overlay aligned Iwith said firstconductor and having a generally zig-zag geometry defining to one sideof said first conductor stable positions for domains when a current of afirst polarity flows in said first conductor and defining to the otherside of said first conductor stable positions for domains Iwhen acurrent of a second polarity flows in said first conductor.

2. A domain propagation arrangement in accordance with claim 1 whereinsaid first magnetic overlay of zigzag geometry is asymmetric to fosterdomain propagation in a first direction and includes therealong curvedareas for defining stable positions for domains propagated therealong.

3. A domain propagation arrangement in accordance with claim 1 whereinsaid first overlay comprises Permalloy.

4. A domain propagation arrangement in accordance with claim 1 alsoincluding means for generating selectively in the plane of said sheet afield in a first or second direction along said first conductor.

5. A domain propagation arrangement in accordance with claim 1 alsoincluding a second electrical conductor spaced apart from said first anda second overlay substantially identical with said first overlaysimilarly defining stable positions for domains when a current flows insaid second conductor.

6. A domain propagation arrangement in accordance with claim 5 alsoincluding means selectively pulsing said first and second conductors.

7. A domain propagation arrangement in accordance with claim 6 includinginput means coupled to said sheet for selectively providing domains instable positions defined by said first and second overlays.

8. A domain propagation arrangement in accordance with claim 7 alsoincluding means coupled to said sheet for selectively detecting thepresence and absence of d0- mains in stable positions defined by saidfirst and second overlays.

9. A domain propagation arrangement in accordance with claim 8 whereinsaid first and second conductors are disposed transverse to one another.

References Cited UNITED STATES PATENTS 3,148,360 9/1964 Hale 340-1743,284,783 11/1966 Davis 340-174 3,460,116 8/1969 Bobeck et al. 340-174STANLEY M. URYNOWICZ, JR., Primary Examiner

